Recently, there has been interest in the use of rubbery, resilient materials for areas which are subject to mechanical shock, such as vehicle bumpers and moldings, exposed corners and surfaces of industrial machines, kickplates and other areas of doors and entrances, and the like. Such resilient materials aid in providing protection against permanent damage. However, in order to attain the desired appearance, a decorative and protective coating must be applied to the surface, and this coating is subject to damage during use. Conventional coatings, including those employed on rubber and similar extensible objects heretofore, do not have the required combination of properties to render them commercially feasible. The requisite properties include extensibility, tensile strength, package stability, film stability, impact resistance, adhesion, chemical and humidity resistance, resistance to cracking under temperature-humidity cycling, sprayability at reasonable solids contents, non-toxicity, and sensitivity to moisture.
It is especially difficult to obtain the above properties in combination since, in most instances, the obtention of one or more of the properties desired requires the use of materials and formulations which under ordinary circumstances tend to make the other desired properties less satisfactory.
Recent developments in this area have produced elastomeric coating compositions which meet the above criteria. These compositions broadly comprise (1) a hydroxyl-containing urethane reaction product of an organic polyisocyanate and a polyhydric material, or, more simply, a polyurethane polyol, and (2) an aminoplast resin. These compositions are storage stable in one package, and when cured, form coatings which are adherent, durable and highly extensible. The coatings are particularly useful on resilient and rubbery substrates, such as EPDM rubber, foam rubber, polyurethane foam and vinyl foam, and on metal surfaces such as mild steel, and aluminum.
While the above-desired coating compositions have many excellent properties, they also have certain disadvantages. In some instances, inadequate adhesion to the substrate has been a problem. When EPDM rubber substrates are used, oily materials seep up (i.e., spew) through the substrate and adversely affect the elastomeric coating, destroying the durability and gloss retention of such coatings.